Drill string stabilizers are tools for resisting lateral loads and lateral movements of the drill collar or drill string in rotary drilling or bore holes in the earth. Certain rock formations and drilling conditions tend to cause the drill bit to deviate from the intended drilling path. Such deviation can be minimized by use of drill string stabilizers. Further, stabilizers properly placed in a drill string for directional drilling can help increase or decrease the bore hole angle as well as maintain a desired hole angle.
Many drill string stabilizers are short pipe sections which are threaded between other parts of the drill string. These cannot always be placed where desired along the length of the drill string and it is desirable to have a stabilizer that can be clamped onto a drill pipe, drill collar or down-hole motor at any location. In addition to permitting stabilization at any desired location, a clamp-on stabilizer can minimize the number of threaded connections in the drill string and each such connection is a site for potential breakage.
When directional drilling with a rotating drill string a near bit stabilizer is commonly positioned immediately above the rock bit and a second string type stabilizer is positioned above a drill collar. The location of the string stabilizer above the rock bit serves a fulcrum which determines whether the hole angle is maintained, increased or decreased. Location is therefore important for obtaining a desired effect. Conventional stabilizers often require and compromise since they are assembled into the drill string between drill collars which are each 30 feet long. Sometimes a short drill collar or pony only ten feet long can be used, but these are not commonly readily available. It is, therefore, desirable to provide a clamp-on stabilizer that can be connected on the outside of the drill collars at any desired location above the rock bit.
Clamp-on stabilizers that have previously been suggested are not satisfactory for field use. Well drilling subjects equipment and tools to very rough handling and sophisticated tools or complicated devices are seldom useful. Prior stabilizers have, for example, required delicate parts or assembly with large numbers of bolts, neither of which is satisfactory on the drill rig floor due to unreliability or great care and time needed for assembly. It is desirable to have a very simple clamp-on stabilizer readily applied on the drill string by the drill rig roughnecks.
Drill strings are subject to becoming out of round due to uneven wearing in the borehole. Such wear can also cause portions of the drill string to wear faster than others, resulting in a variance in outside diameter. Occasionally manufacturing tolerances will permit the outside diameter of the drill string to vary.
Drill string stabilizers that can clamp onto a drill string typically have a small range of tolerance for accepting drill strings of dimensions which vary from the nominal. If the tolerance is exceeded, there is a chance that the stabilizer will not grip the drill string properly and it may be necessary to employ a different tool. It is desirable therefore to provide a stabilizer which has a wide degree of tolerance to accomodate manufacturing differences, uneven wear and out of roundness of a drill string.
It is also desirable to provide a drill string stabilizer which can be made up quickly and positioned at any location on a drill string.
Some prior clamp-on stabilizers have required a breaker or back-up tongs for assembly on the drill string. It is desirable to avoid use of extra tools and provide a clamp-on stabilizer which can be assembled on the drill string using only the set of tongs required for making up the drill string.
It is desirable to provide a clamp-on stabilizer that requires only one location for tightening tongs, thereby minimizing the total length of the stabilizer.
It can also be desirable to provide a clamp-on stabilizer that can be attached to a drill collar that has spiral grooves in its external surface.
Directional drilling with a downhole motor presents special problems for the mineral exploration and production industry. It is often desirable to space a down hole motor from the bottom surface of the non-vertical portion of the hole. Typically, however, such a directional drill motor operates by converting fluid pressure into torque. Such a downhold motor is susceptible to damage if the outside casing is deformed to an out-of-round cross section or is twisted due to differential torque along its length. It is therefore desirable to provide a stabilizer which can be adapted for directional drilling applications and which produces no net torque on a down hole drill motor during operation.